A. Field of the Invention
This invention relates generally to the field of orthodontics. More particularly, the invention relates to a computerized method of creating individual, virtual, three-dimensional tooth models from three-dimensional information of a patient's dentition and a template object. The individual tooth models provide the basis for a computerized, interactive, and orthodontist-controlled treatment planning for a patient suffering from a malocclusion.
B. Description of Related Art
Orthodontics is a field of medicine concerned with the treatment of a patient suffering from a malocclusion or crooked teeth. The traditional approach for correcting the malocclusion is to bond brackets to the teeth and place an orthodontic archwire in the slots of the brackets. The bracket and archwires comprise a force system that causes the teeth to move in a desired fashion to correct the malocclusion. Recently, new types of force systems are coming into vogue, including a series of transparent, removable aligning devices manufactured by Align Technologies.
In dentistry and orthodontics, precise knowledge of a patient's dentition is desirable. The key to efficiency in treatment and maximum quality in results is a realistic simulation of the treatment process. Today's orthodontists have the possibility of taking plaster models of the upper and lower jaw, cutting the cast into single tooth models and sticking these tooth models into a wax bed, lining them up in the desired position, the so-called set-up. This approach allows for reaching a perfect occlusion without any guessing. The next step is to bond a bracket at every tooth model. This would tell the orthodontist the geometry of the wire to run through the bracket slots to receive exactly this result. To make sure that the brackets will be bonded at exactly this position at the real patient's teeth, small templates for every tooth would have to be fabricated that fit over the bracket and a relevant part of the tooth and allow for reliable placement of the bracket at the patient. To increase efficiency of the bonding process, another option would be to transfer each single bracket onto a model of the malocclusion and then fabricate one single transfer tray per jaw that covers all brackets and relevant portions of every tooth. Using such a transfer tray guarantees a very quick and yet precise bonding.
However, it is obvious that such an approach requires an extreme amount of time and labor, and this is the reason why it is limited to scientific environments like orthodontic schools and universities. The normal orthodontist does not fabricate set-ups; he places the brackets directly at the patient to the best of his knowledge, uses an off-the-shelf wire and hopes for the best. While at the beginning of treatment things generally run well as all teeth start to move at least into the right direction, at the end of treatment a lot of time is lost by adaptations and corrections required due to the fact that the end result has not been properly planned at any point of time. For the orthodontist this is still preferable over the lab process described above, as the efforts for the lab process would still exceed the efforts that he has to put in during treatment. And the patient has no choice and does not know that treatment time could be significantly reduced if proper planning was done.
Systems have been proposed in the prior art for scanning the dentition to thereby obtain more precise information about the dentition. U.S. Pat. No. 4,837,732 and U.S. Pat. No. 4,575,805 to Brandestini and Moermann propose a scanning system for in vivo, non-contact scanning of teeth for restorative dentistry. The patents describe a procedure for optically mapping a prepared tooth with a non-contact scan-head. The scan-head delivers the contour data, converted to electrical format, to be stored in a memory. A computer reads the memory following a line scan pattern. A milling device is slaved to follow this pattern by means of position control signals and mills an implant for the prepared tooth cavity. U.S. Pat. No. 5,372,502 to Massen et al. describes an optical probe for measuring teeth that works on the similar principle. As noted in the Massen et al. patent, the Brandestini et al. technique is difficult to use when there are large variations in surface topography since such large jumps displace the pattern by an amount larger than the phase constant of the pattern, making it difficult to reconstruct the pattern of lines. Furthermore, precise knowledge of the angle of incidence and angle of reflection, and the separation distance between the light source and the detector, are needed to make accurate determinations of depth.
U.S. Pat. No. 5,027,281 to Rekow et al. describes a scanning method using a three axis positioning head with a laser source and detector, a rotational stage and a computer controller. The computer controller positions both the rotational stage and the positioning head. An object is placed on a rotating stage and the laser beam reflects from it. The reflected laser beam is used to measure the distance between the object and the laser source. X and Y coordinates are obtained by movement of the rotational stage or the positioning head. A three-dimensional virtual model of the object is created from the laser scanning. The '281 patent describes using this scanning method for scanning a plaster model of teeth for purposes of acquiring shape of the teeth to form a dental prosthesis. The system of the '281 patent is not particularly flexible, since it requires the object to be placed on the rotational stage and precise control of the relative position of the object and the positioning head is required at all times. It is unsuited for in vivo scanning of the teeth.
U.S. Pat. No. 5,431,562 to Andreiko et al. describes a method of acquiring certain shape information of teeth from a plaster model of the teeth. The plaster model is placed on a table and a picture is taken of the teeth using a video camera positioned a known distance away from the model, looking directly down on the model. The image is displayed on an input computer and a positioning grid is placed over the image of the teeth. The operator manually inputs X and Y coordinate information of selected points on the teeth, such as the mesial and distal contact points of the teeth. An alternative embodiment is described in which a laser directs a laser beam onto a model of the teeth and the reflected beam is detected by a sensor. The patent asserts that three-dimensional information as to teeth can be acquired from this technique but does not explain how it would be done. Neither of the techniques of Andreiko have met with commercial success or acceptance in orthodontics. Neither technique achieves in vivo scanning of teeth. Moreover, the video technique does not produce complete three-dimensional information as to the teeth, but rather a limited amount of two-dimensional information, requiring significant operator input. Even using this technique, additional equipment is required even to describe the labial surface of a tooth along a single plane.
In a system such as proposed by Brandestini et al. above, the resulting scanning of the dentition would present both the tooth structure and associated anatomical structures, such as gingival tissue and bone. While this information may be useful for evaluating the current situation, or even designing an implant, it is not directly useable in orthodontic treatment planning since the teeth are not represented as individual objects. Rather, the tooth surfaces are merely part of one continuous surface, including gingival tissue. Orthodontists conceptualize teeth as individual tooth objects that can be moved independently, and the data provided by a scanner of Brandestini et al. do not distinguish between teeth and other objects captured by the scanner.
The present invention solves this problem by providing methods and apparatus for separating individual teeth from other structures in a three-dimensional virtual model. The individual teeth are three-dimensional virtual tooth objects that can be moved or positioned independently from each other. Moreover, the individual tooth objects can be displayed on a computer workstation in context with virtual, three-dimensional orthodontic appliances, such as brackets, archwires, retainers, and transparent removable aligning devices. The individual virtual tooth objects are thus a highly useful tool in orthodontic treatment planning, monitoring, and diagnosis.
The invention is useful for creating individual, virtual three-dimensional tooth models from virtually any source of three-dimensional information of a patient's dentition. For example, the invention will work with CAT scan or laser scanning as the scanning system. The 3-D data can also be obtained from a hand-held optical scanner, such as that described in the above-cited Brandestini et al. patents or something similar. A presently preferred scanning system is described that provides for highly accurate, easy to use, hand-held in-vivo scanning of teeth.